A known process for the flame-retardant treatment of textile materials, including cellulosic (e.g. cotton) materials, consists of impregnation of the material with an aqueous solution of a treatment agent which is a poly(hydroxyorgano)phosphonium compound. This compound may be a salt, for example a tetrakis(hydroxyorgano)phosphonium salt. Alternatively, the compound may be a condensate, for example a condensate of a tetrakis(hydroxyorgano)phosphonium salt with a nitrogen-containing compound such as urea. Following impregnation, the material is dried and then cured with ammonia to produce a cured, water-insoluble polymer which is mechanically fixed within the fibres of the material. After curing, the polymer is oxidised to convert trivalent phosphorus to pentavalent phosphorus and the material is washed and dried.
Such a process is described in, for example, GB2205868, GB 2290562 and GB2294479.
In the curing process ammonia gas may be passed directly into a chamber through which the material passes, or, preferably, ammonia gas is forced through the material inside the chamber. GB1439608 and GB1439609 describe apparatus for use in such a process, which consists of a closed chamber, entry and exit seals thereto through which the material moves, a duct located in the chamber and having one or more orifices through which gaseous ammonia issues and subsequently passes through the material passing over each orifice, the chamber having means to prevent condensed water from dripping on to the material. This type of unit will hereinafter be described as a standard cure unit.
A high speed cure unit is described in GB2252570, where the ammonia feed rate is precisely controlled relative to the amount of material being processed and the curing chamber is pre-filled with ammonia to provide a reservoir of ammonia to allow for any slight variation in the ammonia usage relative to the ammonia input. This type of unit will hereinafter be described as a high speed cure unit.
However, it has been identified that known methods of treating materials with poly(hydroxyorgano)phosphonium compound result in effluent that has significant levels of water soluble phosphorus species present. Water soluble phosphorus species may be considered a hazard. Therefore environmental standards in many countries place limits on the amount of such phosphorus that can be included in waste before it is released to the environment.
This means that when carrying out such methods it is necessary to treat the effluent to remove water soluble phosphorous species, which increases cost and complexity.
Where reference is made to “water soluble phosphorus species” this means species that have a solubility of at least 10 g/l at 25° C.
In particular, the effluent commonly has THPO as the majority water soluble phosphorus species. The removal of this THP salt tends to involve prolonged and harsh oxidation treatments—for example oxidation with hydrogen peroxide under acid conditions or oxidation with hydrogen peroxide under UV.
Therefore there is a need for a technique which enables effluent to be produced that has water soluble phosphorus species present in the form of species that are more readily removed/can be removed without harsh treatment.